juveniles. The results of acute toxicity test showed that the median 96 h lethal concentration (LC₅₀) for Cu²⁺ was 309.74 μg/L. We also measured catalase (CAT) and superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in the soft tissue of clams exposed to 10, 30, or 40 μg/L Cu²⁺, respectively, at 6,12, 24, 48, 72 and 96 h of exposure. CAT activity of the maximum exposed group was lower after 48 h relative to the controls whereas both CAT and SOD activity of all exposure groups were higher at 6, 24, 72 and 96 h. The MDA content was higher in fish exposed to Cu²⁺ than in the control group after 96 h. Our results suggest that exposure to Cu²⁺ causes oxidative damage in juveniles.